SYMPOSIUM
Emerging infectious diseases, animals, and future epidemics
BY HERBERT L. DuPONT, MD
Emerging and reemerging infections have become prevalent in the United States since the 1970s, causing illness, death, and fear among the public. The published literature was reviewed to of- fer a perspective on risk factors for dis- ease acquisition and to allow a predic- tion of the next microbial assault after Ebola and Zika. Four well-integrated factors likely will contribute simulta- neously: animals colonized or infected by pathogens capable of human trans- mission, microbes recurrently chang- ing their virulence, a growing number of susceptible people, and climatic and environmental factors encouraging dis- ease transmission. The next pathogen likely to emerge in an important way in the United States is a new mutant virus arising from a well-established RNA virus family. Standard public health principles, including monitoring general populations for disease, devel- oping new reagents as pathogens arise, implementing control efforts such as effective antibiotic stewardship pro- grams, and vaccine development and administration will minimize damage from the emerging organisms.
INTRODUCTION
Infectious diseases have been impor- tant causes of suffering and death throughout history, with intermittent pandemics that produced millions of deaths. In recent years in Western countries, we continue to see emerg- ing infectious diseases with origins in tropical and semitropical regions with less dramatic health impact for general populations. In this review, we will look at the factors important in emergence and reemergence and consider the role played by animals in human infections. Prediction of the
next disease epidemics will be made along with thoughts about critical public health efforts needed to con- trol future infectious disease threats.
INFECTIOUS DISEASES IN EVOLUTION
An important concept in the history of infectious diseases is that first so- cietal exposure to a virulent microbe may have greater health implications than disease from endemic microor- ganisms. The indigenous populations of Aztecs in Mexico and Incas in Peru lived isolated from other groups. In the early 1500s, Hernando Cortes and Francisco Pizarro and their men and other European colonialists coming from complex integrated societies brought with them smallpox, measles, and other infectious agents to the sus- ceptible Native American populations, resulting in high rates of disease and devastation.1 Measles virus arrived in the Hawai-
ian Islands for the first time in 1848, killing 10 percent to 33 percent of the native population.2
During 1918–19, a
new pandemic strain of H1N1 influ- enza virus of avian origin killed 20 million people worldwide. When the Apollo flights of 1963–72 returned to Earth from the moon, the astronauts were trapped and observed in NASA trailers for three weeks to prevent importation of lunar microbes to sus- ceptible populations on earth. The mobile unit used is on display in the Smithsonian Institute in Washington, D.C.3 In the early 20th century, advances
in water quality, sanitation, vaccines, antibiotics, and reduced fertility rate in the western world were associ- ated with an apparent reduction in serious infections, leading to an era
of optimism about the future burden of infectious diseases. Things began to change when the American Le- gion held its three-day annual meet- ing at the Bellevue-Stratford Hotel in Philadelphia in 1976. The same year, an outbreak of Ebola virus infection occurred in the Democratic Republic of Congo, followed by the first cases of AIDS in 1981 followed a global in- crease in multidrug-resistant tubercu- losis. Group A Streptococcus pyogenes invasive disease emerged in the mid- 1980s.
The myriad subsequent micro-
bial threats seen in rapid succession led the Institutes of Medicine to es- tablish committees to address the problem and prepare for future mi- crobial threats by producing two pub- lications.4,5
The books described the
evolutionary potential of infectious microbes and the complacency of our country with reduced public health awareness, and warned the United States that as we enter the 21st centu- ry we must focus on three elements in the war against microbes: emergence, detection, and response. The Trust for America’s Health
estimated in 2008 that at least 170,000 people in the United States died that year from emerging or reemerging infectious diseases.6
Some of the more
important causes of fatalities in the United States are influenza, with an estimated 36,000 deaths,7
Clostridium difficile infection health care-
associated infections with 99,000 deaths,8
with up to 29,000 associated deaths,9 and foodborne infections with 3,000 deaths per year.10
EMERGING AND REEMERGING INFECTIONS
Emerging infections are those species that have appeared in human populations for the first time or, if reported before, are occurring in greater frequency than before or in new populations not previously involved
Reemerging infections
seen before but that now appear in new locations, in resistant forms, or
February 2017 TEXAS MEDICINE 31
in disease transmission. are those
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